Since their invention over 200 years ago, electrical batteries have become a global multibillion-dollar industry that demonstrates continued growth. Over the last few decades, revolutionary advances have been made in electrochemical storage and conversion devices expanding the capabilities of these systems in a variety of fields including portable electronic devices, transportation, air and space craft technologies, renewable energy technologies, and biomedical devices. Current state of the art electrochemical storage and conversion devices have designs and performance attributes that are specifically engineered to provide compatibility with a diverse range of application requirements and operating environments. For example, advanced electrochemical storage systems have been developed spanning the range from high energy density batteries exhibiting very low self-discharge rates and high discharge reliability for implanted medical devices to inexpensive, light weight rechargeable batteries providing long runtimes for a wide range of portable electronic devices, to high capacity batteries for military and aerospace applications capable of providing extremely high discharge rates over short time periods.
With the expansion and proliferation of personal electronic devices, electric automobiles, and other battery-powered technologies, development of lighter, more efficient, and more powerful battery technologies has been identified as essential for the continued development of these technologies. For example, continued development in the fields of electric vehicles and aerospace engineering has also created a need for mechanically robust, high reliability, high energy density and high power density batteries capable of good device performance in a useful range of operating environments. Furthermore, the demand for miniaturization in the field of consumer electronics and instrumentation continues to stimulate research into novel design and material strategies for reducing the sizes, masses and form factors of high performance batteries.
Batteries may be classified into two categories; disposable or ‘primary’ batteries, and rechargeable or ‘secondary’ batteries. Generally having higher energy densities than secondary batteries, primary batteries such as alkaline and zinc-carbon batteries are often used in portable electronic devices having low current drain. Secondary batteries such as nickel-cadmium, nickel-zinc, nickel metal hydride, and lithium-ion batteries are used in a wide range of applications such as power tools, medical equipment, personal portable electronic devices, and all-electric plug-in vehicles. Although secondary batteries have a higher initial cost than primary batteries, they may be charged very cheaply and used many times, thus having a lower total cost of use. Batteries from both categories consist of a positive electrode (cathode during discharge), a negative electrode (anode during discharge) and an electrolyte. The electrolyte contains ionic species that function as charge carriers for the oxidation and reduction processes occurring at the electrodes. During charge and discharge, electrodes exchange ions with electrolyte and electrons with an external circuit (a load or a charger).
Many recent advances in electrochemical storage and conversion technology are directly attributable to discovery and integration of new materials for battery components. Lithium battery technology, for example, continues to rapidly develop, at least in part, due to the discovery of novel electrode and electrolyte materials for these systems. Development of intercalation host materials for negative electrodes has led to the discovery and commercial implementation of lithium ion based secondary batteries exhibiting high capacity, good stability and useful cycle life. As a result of these advances, lithium based battery technology is currently widely adopted for use in a range of important applications including primary and secondary electrochemical cells for portable electronic systems.
The element lithium has a unique combination of properties that make it attractive for use in an electrochemical cell. First, it is the lightest metal in the periodic table having an atomic mass of 6.94 AMU. Second, lithium has a very low electrochemical oxidation/reduction potential, i.e., −3.045 V vs. NHE (normal hydrogen reference electrode). This unique combination of properties enables lithium based electrochemical cells to have very high specific capacities. Advances in materials strategies and electrochemical cell designs for lithium battery technology have realized electrochemical cells capable of providing useful device performance including: (i) high cell voltages (e.g. up to about 3.8 V), (ii) substantially constant (e.g., flat) discharge profiles, (iii) long shelf-life (e.g., up to 10 years), and (iv) compatibility with a range of operating temperatures (e.g., −20 to 60 degrees Celsius). As a result of these beneficial characteristics, primary lithium batteries are widely used as power sources in a range of portable electronic devices and in other important device applications including, electronics, information technology, communication, biomedical engineering, sensing, military, and lighting.
State of the art lithium ion secondary batteries provide excellent charge-discharge characteristics, and thus, have been widely adopted as power sources in portable electronic devices, such as cellular telephones and portable computers. U.S. Pat. Nos. 6,852,446, 6,306,540, 6,489,055, and “Lithium Batteries Science and Technology” edited by Gholam-Abbas Nazri and Gianfranceo Pistoia, Kluer Academic Publishers, 2004, are directed to lithium and lithium ion battery systems which are hereby incorporated by reference in their entireties.
Charging a secondary battery typically involves passing direct current (d.c.) electricity through the battery in a manner to reverse the discharge process. During charging, electrochemical oxidation of the active material occurs at the positive electrode, while electrochemical reduction takes place at the negative electrode. The charging conditions (e.g., charging voltage, charging current, temperature, overvoltage, etc.) play a significant role in establishing and maintaining the useful lifetime of a battery system. In addition, if current continues to be provided after completion of recharging, the battery may be provided in an overcharge state, which can result in degradation of battery components, for example, via decomposition of electrolyte.
Lithium ion batteries, for example, are commonly charged using the constant-current, constant voltage (CCCV) method. In the CCCV method, the current is held constant typically until the battery voltage reaches a pre-defined value, for example, the voltage in which gassing is likely to begin. At this point, the voltage is held constant while the current is allowed to decline exponentially. In some charging systems, a top-off charge also is provided periodically for certain recharge cycles. In addition to controlling applied constant current and final voltage, charging systems for lithium ion batteries typically monitor and control some battery safety parameters such as temperature and overcharge currents and voltages. In addition, some chargers for these batteries also take into account the battery cycle life to adjust the CCCV conditions. Occasionally, linear voltammetry (LV) is used in systems and methods to charge batteries, such as lithium ion batteries, wherein a charging voltage is applied that varies linearly with time over a minimum and maximum voltage range.
Many state of the art CCCV and LV procedures and systems for charging lithium ion batteries, however, fail to take into account certain system parameters that can significantly impact cycling performance and battery lifetime. These parameters include, for example, the battery ‘state of health’ (SOH), and/or the health and/or composition of specific system components such as the anode, cathode, and electrolyte (See, e.g., US 2010/0090650). The SOH varies with the system ‘history’, such as for the most common charge/discharge cycles, overcharge and over-discharge, and thermal aging. In some instances, for example, degradation of one of the active components: anode, cathode and electrolyte, affects the cell's SOH. The failure of state of the art charging systems to take into account the SOH, for example, may result in premature battery aging and irreversible losses in stored energy upon cycling.
As will be clear from the foregoing, there exists a need in the art for an improved methods and systems for charging batteries. Specifically, chargers and charging methods are needed that take into account system parameters that can affect cycling performance and battery lifetime, such as the battery's SOH and the health and/or composition of system components.